A belt type continuously variable transmission is a known transmission mounted on a vehicle or the like. The belt type continuously variable transmission includes a first pulley that receives driving force from an internal combustion engine, a second pulley coupled to a vehicle wheel, and a belt running around the two pulleys. The continuously variable transmission changes the winding radius of the belt at each pulley to change the gear ratio in a continuous and stepless manner.
Such a belt type continuously variable transmission changes the hydraulic pressure of a hydraulic pressure chamber arranged in each pulley to change the balance of thrusts, which is the force that sandwiches the belt. This changes the winding ratio of the belt at each pulley and controls the gear ratio.
To this end, such a continuously variable transmission includes a hydraulic pressure controller that controls the hydraulic pressure supplied to each pulley. The hydraulic pressure controller includes a plurality of solenoid valves, which are driven based on an electrical drive command, and a plurality of control valves, which are driven by a driving hydraulic pressure output from the solenoid valves. The hydraulic pressure controller drives the control valves based on drive commands output from an electronic control unit to supply hydraulic oil to the hydraulic pressure chamber of each pulley or discharge hydraulic oil from the hydraulic pressure chamber of each pulley thereby controlling the hydraulic pressure of the hydraulic pressure chamber in each pulley.
In the hydraulic pressure controller for the continuously variable transmission, a regulator valve adjusts the hydraulic pressure of the hydraulic oil discharged from an oil pump and generates line pressure, which is the originating pressure of the hydraulic pressure to output from the control valves. The line pressure is input to the control valves, and the line pressure is adjusted by the control valves to generate the hydraulic pressure supplied to each pulley.
In the hydraulic pressure controller described above, a drive load of the oil pump becomes high when the line pressure becomes high. Thus, a hydraulic pressure controller for a continuously variable transmission that is described in patent document 1 feedback-adjusts the line pressure in accordance with the level of the hydraulic pressure supplied to each pulley.
Specifically, hydraulic pressure corresponding to the level of the hydraulic pressure supplied to each pulley is input to the regulator valve. The line pressure is increased when the hydraulic pressure supplied to each pulley is high, and the line pressure is decreased when the hydraulic pressure supplied to each pulley is low.
In this manner, by feedback adjusting the line pressure in accordance with the level of the hydraulic pressure supplied to each pulley, an excessive increase in the drive load of the oil pump when the line pressure increases more than necessary is suppressed.